Method of manufacturing high-pressure tank and high-pressure tank

ABSTRACT

A high-pressure tank in a method of manufacturing a high-pressure tank includes a liner and a fiber. The manufacturing method includes: preparing a dome and a pipe each having a general portion and a joining end portion formed to be thicker than the general portion such that an outer diameter at least at an end face is larger than an outer diameter of the general portion by an estimated level difference amount; joining the joining end portion of the dome and the joining end portion of the pipe together in an axial direction; cutting off portions on the further outer side in a radial direction than a reference plane, with an outer peripheral surface of the general portion of the dome having a large outer diameter at the joined surface as the reference plane; and winding a carbon fiber around the outer peripheral surface of the liner in helical winding.

INCORPORATION BY REFERENCE

This application is a divisional application of U.S. patent applicationSer. No. 16/520,685 filed on Jul. 24, 2019, which claims the benefit ofJapanese Patent Application No. 2018-175615 filed on Sep. 20, 2018, thecontents of which including the specification, drawings and abstract isincorporated herein by reference in its entirety.

BACKGROUND 1. Technical Field

The present disclosure relates to a method of manufacturing ahigh-pressure tank and a high-pressure tank, and in particular, to amethod of manufacturing a high-pressure tank in which a fiber is woundaround an outer periphery of the liner made by joining a plurality ofparts together, and a high-pressure tank.

2. Description of Related Art

As a method of manufacturing a high-pressure tank, a filament windingmethod in which a high-strength outer shell is formed by winding a fiberaround the outer periphery of a liner configuring an inner shell hasbeen known in the past.

A fiber winding method in the filament winding method is classifiedroughly into hoop winding in which a fiber is wound at substantiallyright angles with respect to a liner center line, and a helical windingin which a fiber is wound at a predetermined angle (fiber angle) withrespect to a liner center line.

In such a filament winding method, it is known that strength is improvedwhen winding is performed such that the tension of a fiber becomesconstant. However, in the case of the helical winding, fibers areconcentrated at an end portion of the liner according to folding-back ofthe fibers, so that a fiber layer becomes thicker than the otherportions, and therefore, there is a problem in that the shape of the endportion deviates from an even tension curved surface as the winding ofthe fiber is repeated.

Therefore, for example, Japanese Unexamined Patent ApplicationPublication No. 2016-217466 (JP 2016-217466 A) proposes the shape of adome portion having a predetermined curved surface different from aneven tension curved surface, in which an even tension curved surface isformed in a process of winding a fiber with helical winding, in ahigh-pressure tank having a hemispherical dome portion at an end portionof the liner.

SUMMARY

Incidentally, the liner configuring an inner shell of the high-pressuretank is usually formed in a tubular hollow body in which both ends aresubstantially closed, and therefore, at least one joined portion isformed. For example, when bottomed cylindrical parts (hereinafter alsoreferred to as “domes”) are joined together in an axial direction, onejoined portion is formed, and, for example, when a cylindrical part(hereinafter also referred to as a “pipe”) is interposed between twodomes and joined to the two domes in the axial direction, two joinedportions are formed.

Then, although it is not mentioned in JP 2016-217466 A, it is knownthat, even though parts such as a dome and a pipe are molded products, alevel difference inevitably occurs at a joined portion between the partsdue to variation in the shrinkage factor of a material, misalignment atthe time of joining, or the like. In this way, when a fiber is woundaround the outer periphery of the liner in a state where a leveldifference is generated at the joined portion, there is a case where aharmful gap in which the strength is lowered is formed between the fiberand the liner.

Therefore, it is conceivable to cut off the level difference, based onthe outer diameter of the part having a small outer diameter at a joinedsurface. However, in this case, there is a problem in that the thicknessof the cut-off part (the part having a large outer diameter at thejoined surface) is thinned (it becomes difficult to secure the minimumplate thickness).

The present disclosure provides a technique for suppressing occurrenceof a harmful gap between a liner and a fiber while the minimum platethickness of the liner is secured, in a method of manufacturing ahigh-pressure tank in which the fiber is wound around an outer peripheryof the liner made by joining a plurality of parts together, and thehigh-pressure tank.

In the method of manufacturing a high-pressure tank and thehigh-pressure tank of the present disclosure, the shape of an endportion of a part configuring a joined portion in a liner is optimized.

A first aspect of the present disclosure relates to a method ofmanufacturing a high-pressure tank. The high-pressure tank includes aliner formed by joining a plurality of cylindrical liner constituentmembers together, and a fiber wound around an outer periphery of theliner. (In this specification, a “cylindrical shape” is meaningincluding a “substantially cylindrical shape”).

The manufacturing method includes preparing the cylindrical linerconstituent members each having a cylindrical general portion and ajoining end portion formed to be thicker than the cylindrical generalportion such that, in a case where an estimated value of an amount of alevel difference that is generated at a joined surface where the linerconstituent members are joined together is set to be an estimated leveldifference amount, an outer diameter at least at an end face is largerthan an outer diameter of the cylindrical general portion by theestimated level difference amount, as the cylindrical liner constituentmembers.

The manufacturing method includes joining the joining end portion of oneof the cylindrical liner constituent members and the joining end portionof another one of the cylindrical liner constituent members together inan axial direction, cutting off portions on a further outer side in aradial direction than a reference plane, in both the joining endportions joined together, with an outer peripheral surface of thecylindrical general portion having a large outer diameter at the joinedsurface, out of the liner constituent members joined together, as thereference plane, and winding the fiber around an outer peripheralsurface of the cylindrical liner in helical winding.

In the present disclosure, the “cylindrical liner constituent member”includes not only a cylindrical liner constituent member with both endsopen but also a bottomed cylindrical liner constituent member or thelike, which has a hemispherical dome portion at one end of a cylindricalportion, for example.

According to the first aspect of the present disclosure, the outerdiameter at the end face of the cylindrical liner constituent member islarger than the outer diameter of the cylindrical general portion by theestimated level difference amount, and therefore, when the portionfurther on the outer side in the radial direction than the referenceplane (the outer peripheral surface of the cylindrical general portion)is cut off after joining, the amount corresponding to a rising height(=estimated level difference amount) at the joined surface is cut off.Therefore, it is possible to reliably cut off the level difference atthe joined surface, which has occurred within the range of the estimatedlevel difference amount, and in this way, it is possible to suppressoccurrence of a harmful gap, in which the strength is lowered, betweenthe liner and the fiber.

According to the first aspect of the present disclosure, the portionfurther on the outer side in a radial direction than the outerperipheral surface (the reference plane) of the cylindrical generalportion of the cylindrical liner constituent member having a large outerdiameter at the joined surface is cut off, whereby an end portion havingthe same thickness as that of the cylindrical general portion(hereinafter also referred to as a “first joining end portion”) isformed on the side of the liner constituent member having a larger outerdiameter and an end portion having a larger outer diameter than thecylindrical general portion and being thicker than the cylindricalgeneral portion (hereinafter also referred to as a “second joining endportion”) is formed on the side of the cylindrical liner constituentmember having a smaller outer diameter. Therefore, a portion thatbecomes thinner in thickness than the cylindrical general portion is notgenerated, and therefore, it is possible to secure the minimum platethickness of the liner.

According to the first aspect of the present disclosure, it is possibleto suppress occurrence of a harmful gap between the liner and the fiberwhile the minimum plate thickness of the liner is secured.

Incidentally, for example, in a configuration in which the joining endportion before joining is formed into a cylindrical shape having alarger outer diameter than the cylindrical general portion and beingthicker than the cylindrical general portion and the joining end portionand the cylindrical general portion are connected to each other by astepped surface, there is a case where a large stepped surface remainsat the boundary between the second joining end portion and thecylindrical general portion after the joining. In this case, even thoughthere is no level difference at the joined surface between the firstjoining end portion and the second joining end portion, there is a casewhere a harmful gap occurs between the liner and the fiber at theboundary (the stepped surface) between the second joining end portionand the cylindrical general portion. On the other hand, in a case wherethe joining end portion before joining is made in a tapered shape, forexample, when the cylindrical liner constituent member is joined bymelting the joining end portion, the thickness (cross-sectional area) ofthe joining end portion changes, and therefore, there is a problem inthat it is difficult to make a joining processing condition such as aheat input amount constant.

In the method according to the first aspect, the joining end portionbefore joining may have a cylindrical joining margin portion located atan extreme end portion of the joining end portion and having an outerdiameter larger than the outer diameter of the general portion by theestimated level difference amount, and a tapered portion having an outerdiameter that decreases from the joining margin portion toward thecylindrical general portion so as to connect an outer peripheral surfaceof the joining margin portion and an outer peripheral surface of thecylindrical general portion, and the joining end portions of therespective cylindrical liner constituent members may be joined togetherby melting the joining margin portions of the respective cylindricalliner constituent members.

According to the first aspect of the present disclosure, the taperedportion is provided at the joining end portion, whereby the closer tothe cylindrical general portion, the smaller the difference between theouter diameter of the second joining end portion and the outer diameterof the cylindrical general portion becomes, and therefore, it ispossible to suppress occurrence of a harmful gap between the liner andthe fiber not only at the joined surface between the first joining endportion and the second joining end portion but also at the boundarybetween the second joining end portion and the cylindrical generalportion. In addition, the cylindrical joining margin portion having aconstant thickness (cross-sectional area) is provided at the extreme endportion of the joining end portion, and therefore, when the joining endportions of the respective cylindrical liner constituent members arejoined together by melting the joining margin portions of the respectiveliner constituent members, it is possible to make it easier to make ajoining processing condition such as a heat input amount constant.

However, even though a tapered portion is provided at the joining endportion, when the inclination angle of the tapered portion is extremelylarge, there is a case where a harmful gap occurs between the liner andthe fiber at the time of filament winding, and on the other hand, whenthe inclination angle of the tapered portion is extremely small, thereis a case where the second joining end portion is lengthened more thanis needed and useless thickening of the liner occurs.

In the method according to the first aspect, an inclination angle of thetapered portion may be set so as to satisfy a relationship of anfollowing expression, tan θ=t×tan ψ/(R×(1−R²/(R+t)²)^(1/2)). Here, θ maybe the inclination angle of the tapered portion, t may be the estimatedlevel difference amount, ψ may be a fiber angle of the fiber withrespect to a center line of the liner in the winding, and R may be anouter circumference radius of the cylindrical general portion.

According to the first aspect of the present disclosure, by defining theinclination angle of the tapered portion in association with theperformance of the high-pressure tank (the outer circumference radius Rrelated to the storage amount of the high-pressure tank, the fiber angleψ related to the strength of the high-pressure tank, and t related tothe level difference amount), it is possible to optimize the inclinationangle of the tapered portion in the high-pressure tank having the neededperformance and to minimize the gap between the liner and the fiber.

In the method according to the first aspect, the inclined surfaces ofthe tapered portions of the respective liner constituent members may bestepped down to the outer peripheral surfaces of the general portionsbefore the inclined surfaces intersect the outer peripheral surfaces ofthe cylindrical general portions, and the joining end portions of therespective cylindrical liner constituent members may be joined togetherin a state where the cylindrical general portions of the respectivecylindrical liner constituent members are gripped and fixed.

When the difference between the outer diameter of the tapered portionthat is reduced in diameter and the outer diameter of the generalportion becomes sufficiently small, it is not needed to extend theinclined surface until it intersects (is connected to) the outerperipheral surface of the cylindrical general portion. In this respect,according to the aspect of the present disclosure, the inclined surfaceof the tapered portion is stepped down before it intersects the outerperipheral surface of the cylindrical general portion, and therefore, itis possible to shorten the tapered portion (lengthen the general portionthat is a regular dimension portion), and in this way, it is possible tosuppress useless thickening and improve a yield. Further, the boundarybetween the joining end portion and the cylindrical general portion canbe easily understood when the cylindrical general portion is gripped andfixed, and therefore, the joining processing can be easily performed. Inaddition, the tapered portion is made short, and therefore, even thoughthe cylindrical general portion that is easier to be gripped than thetapered portion is gripped and fixed, it is possible to bring a fixingposition close to the joined surface, and in this way, it is possible toimprove positioning precision.

A second aspect of the present disclosure relates to a high-pressuretank. The high-pressure tank includes a liner configured by joining aplurality of cylindrical liner constituent members together, and a fiberwound around an outer periphery of the liner.

The liner includes cylindrical general portions, and a joined portionconfigured by joining joining end portions of the liner constituentmembers together in an axial direction, the joined portion includes afirst joining end portion and a second joining end portion, of whichouter diameters at a joined surface are equal to each other, the firstjoining end portion has the same thickness as the thickness of thecylindrical general portion, and the second joining end portion has alarger outer diameter than the cylindrical general portion and isthicker than the cylindrical general portion.

According to the second aspect of the present disclosure, the joinedportion is configured of the first joining end portion and the secondjoining end portion, in which the outer diameters at the joined surfaceare equal to each other, and therefore, it is possible to suppressoccurrence of a harmful gap between the liner and the fiber. Further,since the first joining end portion has the same thickness as that ofthe cylindrical general portion and the second joining end portion has alarger outer diameter than the cylindrical general portion and isthicker than the cylindrical general portion, it is possible to securethe minimum plate thickness of the liner.

According to the second aspect of the present disclosure, a leveldifference inevitably occurs at the joined surface between the linerconstituent members due to variation in the shrinkage factor of amaterial, misalignment at the time of joining, or the like. However,with the method of manufacturing a high-pressure tank, it is possible tosuitably realize the joined portion according to the second aspect ofpresent disclosure, which is configured of the first joining end portionhaving the same thickness as that of the cylindrical general portion andthe second joining end portion having a larger outer diameter than thecylindrical general portion and being thicker than the cylindricalgeneral portion, the first joining end portion and the second joiningend portion having the outer diameters equal to each other at the joinedsurface.

In the high-pressure tank according to the second aspect, the secondjoining end portion may include a tapered portion having an outerdiameter that decreases with increasing distance in the axial directionfrom the joined surface.

According to the second aspect of the present disclosure, the closer tothe cylindrical general portion, the smaller the difference between theouter diameter of the second joining end portion and the outer diameterof the cylindrical general portion becomes, and therefore, even at theboundary between the second joining end portion and the cylindricalgeneral portion, occurrence of a harmful gap between the liner and thefiber can be suppressed.

In the high-pressure tank according to the second aspect, an inclinedsurface of the tapered portion may be stepped down to an outerperipheral surface of the general portion before the inclined surfaceintersects the outer peripheral surface.

According to the second aspect of the present disclosure, it is possibleto shorten the tapered portion (lengthen the general portion that is aregular dimension portion), and in this way, it is possible to suppressuseless thickening and improve a yield.

According to the aspects of the present disclosure, with the method ofmanufacturing a high-pressure tank and the high-pressure tank of thepresent disclosure, it is possible to suppress occurrence of a harmfulgap between the liner and the fiber while the minimum plate thickness ofthe liner is secured.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance ofexemplary embodiments of the present disclosure will be described belowwith reference to the accompanying drawings, in which like numeralsdenote like elements, and wherein:

FIG. 1 is a sectional view schematically showing a high-pressure tankaccording to an embodiment of the present disclosure;

FIG. 2A is a sectional view schematically showing a liner constituentmember and shows a dome;

FIG. 2B is a sectional view schematically showing a liner constituentmember and shows a pipe;

FIG. 2C is a sectional view schematically showing a liner constituentmember and shows a dome;

FIG. 3A is a sectional view schematically showing a liner and shows theentire liner;

FIG. 3B is a sectional view schematically showing a liner and shows ajoined portion in an enlarged manner;

FIG. 4A is a diagram schematically describing a method of winding afiber in a filament winding method and shows helical winding;

FIG. 4B is a diagram schematically describing a method of winding afiber in a filament winding method and shows hoop winding;

FIG. 5 is a sectional view schematically showing a joining end portionof a liner constituent member before joining;

FIG. 6A is a diagram schematically describing a method of manufacturinga high-pressure tank and shows a joining process;

FIG. 6B is a diagram schematically describing the method ofmanufacturing a high-pressure tank and shows a joining process;

FIG. 6C is a diagram schematically describing the method ofmanufacturing a high-pressure tank and shows a cutting-off process;

FIG. 7 is a sectional view schematically showing a joined portion aroundwhich a fiber is wound;

FIG. 8 is a conceptual diagram schematically describing a geometricrelationship between a fiber angle and an inclination angle;

FIG. 9 is a conceptual diagram schematically describing a relationshipbetween a gap between a liner and a carbon fiber, and a set inclinationangle;

FIG. 10 is a graph schematically showing the relationship between thegap between the liner and the carbon fiber, and the set inclinationangle;

FIG. 11 is a sectional view schematically showing an end portion of apipe according to Modification Example 1;

FIG. 12 is a sectional view schematically showing an end portion of apipe according to Modification Example 2;

FIG. 13 is a diagram schematically describing a joined portion of aliner of the related art; and

FIG. 14 is a diagram schematically describing the joined portion of theliner of the related art.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, a mode for carrying out the present disclosure will bedescribed with reference to the drawings.

High-Pressure Tank

FIG. 1 is a sectional view schematically showing a high-pressure tank 1according to this embodiment. As shown in FIG. 1, the high-pressure tank1 includes a cylindrical liner 3 as an inner shell, a carbon fiber 5which forms an outer shell by being laminated by being wound around theouter periphery of the liner 3, and aluminum caps 7, 9 that areassembled to both ends of the liner 3 by press fitting.

The liner 3 is made of resin and is composed of three split-formedcylindrical liner constituent members 10, 20, 30, as shown in FIG. 1.Specifically, the liner 3 is configured by interposing one pipe 20between two domes 10, 30 and joining the pipe and the domes together inan axial direction.

FIGS. 2A to 2C are sectional views schematically showing the linerconstituent members 10, 20, 30, in which FIGS. 2A and 2C show the domes10, 30 and FIG. 2B shows the pipe 20. Each of the domes 10, 30 is formedin a bottomed cylindrical shape. More specifically, the domes 10, 30have cylindrical general portions 11, 31, hemispherical dome portions12, 32 that are provided so as to close first ends of the generalportions 11, 31 and to which the caps 7, 9 are assembled, and joiningend portions 13, 33 provided at second ends of the general portions 11,31. On the other hand, the pipe 20 is formed in a cylindrical shape withboth ends opened and has a cylindrical general portion 21 and joiningend portions 23 provided at both ends of the general portion 21. In thedomes 10, 30 and the pipe 20, the outer diameters and the innerdiameters thereof in the general portions 11, 21, 31 are formed with thesame design value. Further, the joining end portions 13, 23, 33 are alsoformed with the same shape and dimension.

The dome 10 and the pipe 20 are joined together by an infrared weldingmethod in which each of the extreme end portion of the joining endportion 13 and the extreme end portion of the joining end portion 23 isheated and melted by infrared rays and both the extreme end portions arethen pressure-bonded to each other. Similarly, the pipe 20 and the dome30 are joined together by an infrared welding method in which each ofthe extreme end portion of the joining end portion 23 and the extremeend portion of the joining end portion 33 is heated and melted byinfrared rays and both the extreme end portions are then pressure-bondedto each other. Then, a protruding protrusion (a bead 50 or the like(refer to FIG. 6B)) according to the joining is treated by grinding orthe like, whereby a joined portion 40 is formed.

FIGS. 3A and 3B are sectional views schematically showing the liner 3,in which FIG. 3A shows the entire liner 3 and FIG. 3B shows the joinedportion 40 in an enlarged manner. In FIG. 3B, a stepped surface 23 b(described later) is not shown.

As described above, the domes 10, 30 and the pipe 20 are joined togetherby the infrared welding method, whereby the liner 3 of this embodimenthas the dome portions 12, 32 at both ends, three cylindrical generalportions 11, 21, 31, and two joined portions 40, as shown in FIG. 3A.Further, each of the joined portions 40 is configured of a first joiningend portion 13′ and a second joining end portion 23′, in which the outerdiameters at a joined surface 40 a are equal to each other, as shown inFIG. 3B. The first joining end portion 13′ has the same thickness asthat of the general portion 11, whereas the second joining end portion23′ has a larger outer diameter than the general portion 21 and isformed to be thicker than the general portion 21. Details of the joinedportion 40 will be described later.

FIGS. 4A and 4B are diagrams schematically describing a method ofwinding a carbon fiber 5 in a filament winding method, in which FIG. 4Ashows helical winding and FIG. 4B shows hoop winding. In thehigh-pressure tank 1 of this embodiment, the outer shell is formed bywinding the carbon fiber 5 around the outer periphery of the liner 3 bythe filament winding method. In this embodiment, the helical winding inwhich the carbon fiber 5 is wound at a predetermined angle with respectto a liner center line AX, as shown in FIG. 4A, and the hoop winding inwhich the carbon fiber 5 is wound substantially at right angles withrespect to the liner center line AX, as shown in FIG. 4B, are usedtogether.

Specifically, after the lowermost layer is wound with the helicalwinding, an upper layer is wound with the hoop winding. In this way, thedome portions 12, 32 can be mainly protected by the carbon fibers 5 thatare wound with oblique crossing with respect to the caps 7, 9 at bothends at the time of the helical winding, and the general portions 11,21, 31 can be mainly protected by the carbon fibers 5 that are woundwith the hoop winding. In the helical winding, since the carbon fibers 5are wound with oblique crossing with respect to the caps 7, 9 at bothends, an extending direction of the carbon fiber 5 is oblique withrespect to the liner center line AX, and the angle is referred to as afiber angle ψ.

Joined Portion

Next, the joined portion 40 will be described in detail. However, inorder to make it easy to understand the present disclosure, a joinedportion in the related art will be described before the description ofthe joined portion 40.

FIGS. 13 and 14 are diagrams schematically describing a joined portion140 of a liner 103 of the related art. In FIGS. 13 and 14, a case wherethe outer diameter of a dome 110 is large at a joined surface 140 a isexemplified. However, of course, there is also a case where the outerdiameter of a pipe 120 is made large.

In the dome 110 and the pipe 120 of the related art, the joining endportions 13, 23 as in this embodiment are not provided, and end portionsof general portions 111, 121 are directly joined together by theinfrared welding method. The dome 110 and the pipe 120 are formed suchthat the outer diameters and the inner diameters in the general portions111, 121 have the same design values. However, even in a molded product,a level difference S inevitably occurs between an outer peripheralsurface 111 a and an outer peripheral surface 121 a (and an innerperipheral surface 111 b and an inner peripheral surface 121 b) at thejoined surface 140 a due to variation in the shrinkage factor of amaterial, misalignment at the time of joining, or the like. When thecarbon fiber is wound around the outer periphery of the liner 103 in astate where the level difference S is generated in the joined portion140 in this manner, a harmful gap that reduces strength is createdbetween the carbon fibers and the liner 103.

For this reason, in order to reduce the level difference S, as shown inFIG. 14, it is conceivable to cut off an outer peripheral portion of thedome 110 having a large outer diameter such that the level difference Sat the joined surface 140 a disappears. However, in this case, thethickness of the dome 110 becomes thin in a cut-off section L, and thusthere is a problem in that it becomes difficult to secure the minimumplate thickness of the liner 103.

Therefore, in the high-pressure tank 1 of this embodiment, the shapes ofthe joining end portions 13, 23, 33 configuring the joined portion 40 ofthe liner 3 are optimized. As described above, the joining end portions13, 23, 33 have the same shape and dimension, and therefore, in thefollowing, the joining end portion 23 of the pipe 20 will be describedand the joined portion 40 in which the joining end portion 13 of thedome 10 and the joining end portion 23 of the pipe 20 are joinedtogether will be described.

FIG. 5 is a sectional view schematically showing the joining end portion23 of the pipe 20 before joining. In this embodiment, the joining endportion 23 is formed in a thickness (T+t) thicker than a thickness T ofthe general portion 21 such that the outer diameter at least at an endface 23 a becomes larger than the outer diameter of the general portion21 by an estimated level difference amount t. Here, the “estimated leveldifference amount t” is an estimated value of a level difference amountthat can be generated at each of the joined surfaces 40 a joining theliner constituent members 10, 20, 30 together, and is calculated usingCAD in anticipation of variation in the shrinkage factor of a material,misalignment, or the like.

More specifically, as shown in FIG. 5, the joining end portion 23 has acylindrical joining margin portion 27 located at the extreme end portionof the joining end portion 23 and having an outer diameter larger thanthe outer diameter of the general portion 21 by the estimated leveldifference amount t, and a tapered portion 25 having an outer diameterthat decreases at an inclination angle θ from the joining margin portion27 toward the general portion 21 so as to connect an outer peripheralsurface 27 a of the joining margin portion 27 and an outer peripheralsurface 21 a of the general portion 21. A section length L1 of thejoining margin portion 27 is set to the amount of heat-melting at thetime of infrared welding, and the deformation of the bead 50 or thelike, which is formed according to the joining, is completed within thesection length L1. That is, the joining margin portion 27 is convertedinto the bead 50 or the like by being joined by heat-melting, so that itdoes not remain at the joined portion 40 after the joining.

Further, an inclined surface 25 a of the tapered portion 25 is steppeddown to the outer peripheral surface 21 a of the general portion 21before it intersects (is connected to) the outer peripheral surface 21a. In other words, the inclined surface 25 a of the tapered portion 25and the outer peripheral surface 21 a of the general portion 21 areconnected through the stepped surface 23 b. In this way, a sectionlength L2 of the tapered portion 25 can be shortened as compared with acase where the inclined surface 25 a of the tapered portion 25intersects the outer peripheral surface 21 a of the general portion 21.The height of the stepped surface 23 b is set to the maximum value (forexample, 0.4 (mm)) of an allowable range of a gap between the liner 3and the carbon fiber 5 (a range of a gap that does not cause a decreasein strength).

The joining end portion 23 configured as described above is joined tothe joining end portion 13 having the same configuration in thefollowing procedure. FIGS. 6A to 6C are diagrams schematicallydescribing a method of manufacturing a high-pressure tank 1, in whichFIGS. 6A and 6B show a joining process and FIG. 6C shows a cutting-offprocess.

In the joining process, the joining end portion 13 of the dome 10 andthe joining end portion 23 of the pipe 20 are joined together in theaxial direction. More specifically, first, as shown by a shaded portionin FIG. 6A, a joining margin portion 17 in the joining end portion 13 ofthe dome 10 and the joining margin portion 27 in the joining end portion23 of the pipe 20 are heated and melted by infrared rays. At this time,the joining margin portions 17, 27 are formed in a cylindrical shape,that is, a shape in which the cross-sectional area does not change, andtherefore, a change in the amount of heating as in, for example, a caseof joining the tapered portions 15, 25 together is not needed, so thatit is easy to make a joining processing condition such as a heat inputamount constant.

Next, as shown in FIG. 6B, the dome 10 and the pipe 20 are gripped andfixed by jigs 60 and are pressure-bonded to each other. In a case ofgripping and fixing the dome 10 and the pipe 20 with the jigs 60, theflat general portions 11, 21 are easier to be gripped than the taperedportions 15, 25, and therefore, in this embodiment, the stepped surfaces13 b, 23 b are provided, whereby it becomes easy to recognize theboundary between each of the tapered portions 15, 25 and each of thegeneral portions 11, 21. Further, the stepped surfaces 13 b, 23 b areprovided, whereby the section length L2 of the tapered portion 25 isshortened, so that it is possible to lengthen the general portions 11,21 that are regular dimension portions, and in addition, even though thegeneral portions 11, 21 are gripped and fixed by the jigs 60, a fixingposition can be brought closer to a welded portion, and in this way, itis possible to improve positioning precision.

In this manner, when the dome 10 and the pipe 20 are joined together bythe infrared welding method, as shown in FIG. 6B, the beads 50 convertedfrom the molten joining margin portions 17, 27 are formed inside andoutside the joined portion. However, the bead 50 on the outer side iscut off together with the level difference S in the subsequentcutting-off process.

In the cutting-off process, an outer peripheral surface 11 a of thegeneral portion 11 of the dome 10 that is the liner constituent memberhaving a larger outer diameter at the joined surface 40 a, out of theliner constituent members 10, 20 joined together in the joining process,is set as a reference plane, and portions further on the outer side in aradial direction than the reference plane (the outer peripheral surface11 a), of the joining end portions 13, 23 joined together in the joiningprocess, are cut off. Here, the joining end portions 13, 23 arethickened by the estimated level difference amount t at the end faces 13a, 23 a, and therefore, when the portion further on the outer side inthe radial direction than the reference plane is cut off, it is possibleto surely cut off the level difference S at the joined surface 40 a,which is generated within the range of the estimated level differenceamount t. In this way, as shown in FIG. 6C, the joined portion 40 thatis composed of the first joining end portion 13′ having the samethickness as that of the general portion 11 and the second joining endportion 23′ having a larger outer diameter than the general portion 21and being thicker than the general portion 21, in which the outerdiameters of the first joining end portion 13′ and the second joiningend portion 23′ at the joined surface 40 a are equal to each other, thatis, the joined portion 40 similar to that shown in FIG. 3B is formed. Ina case where the level difference S is relatively small, a part of thetapered portion 25 (a difference between the estimated level differenceamount t and the level difference S) is also cut off, as shown in FIG.6C. However, in a case where the level difference S is equal to theestimated level difference amount t, as shown in FIG. 3B, the taperedportion 25 is not cut off and remains as it is.

The carbon fiber 5 is wound around the outer peripheral surface of theliner 3 formed in this way and, for example, as shown in FIG. 3B, by thehelical winding, whereby it is possible to obtain the joined portion 40in which a harmful gap (a gap that reduces the strength of thehigh-pressure tank 1) is not generated between the liner 3 and thecarbon fiber 5, while securing the minimum plate thickness of the liner3 (having a plate thickness equal to or greater than the thickness T atany part of the liner 3), as shown in FIG. 7.

However, when the inclination angle θ of the tapered portion 25 thatremains at the second joining end portion 23′ is extremely large, thereis a case where a harmful gap is generated between the liner 3 and thecarbon fiber 5 at the time of the filament winding, and on the otherhand, when the inclination angle θ of the tapered portion 25 isextremely small, there is a case where the second joining end portion23′ is lengthened more than is needed and useless thickening occurs.

Therefore, in this embodiment, the inclination angle θ of the taperedportion 25 is set so as to satisfy the relationship of Expression 1 byusing the estimated level difference amount t and the fiber angle ψ in acase where the outer circumference radius of the general portion 21 isR.

tan θ=t×tan ψ/(R×(1−R ²/(R+t)²)^(1/2))  (Expression 1)

Hereinafter, this Expression 1 will be described.

FIG. 8 is a conceptual diagram schematically describing a geometricrelationship between the fiber angle ψ and the inclination angle θ. InFIG. 8, a top view in a state where the carbon fiber 5 is wound aroundthe liner 3 with the helical winding, a side view of the tapered portion25 of the second joining end portion 23′, and an axial view of thesecond joining end portion 23′ are arranged in order from the top in thesame plane. A reference numeral 40 b in the axial view is an imaginaryline in a case where it is assumed that the second joining end portion23′ does not rise radially outward by the estimated level differenceamount t at the joined surface 40 a, and the radius of the imaginaryline 40 b coincides with the outer circumference radius R of the generalportion 21. Therefore, in the side view, the imaginary line 40 b and theouter peripheral surface 21 a of the general portion 21 are flush witheach other.

In FIG. 8, a state where the condition regarding the gap between theliner 3 and the carbon fiber 5 is the worst, in other words, a statewhere the tapered portion 25 is not cut off and a rising height(=estimated level difference amount t) at the joined surface 40 aremains as it is, is assumed. Further, a state where the inclinedsurface 25 a of the tapered portion 25 is not stepped down and extendsobliquely from the joined surface 40 a by a section length d2 tointersect the outer peripheral surface 21 a of the general portion 21 isassumed. In such a state, the above Expression 1 expressing thegeometrical relationship between the fiber angle ψ and the inclinationangle θ in a case where the gap between the liner 3 and the carbon fiber5 is assumed to be 0 is calculated.

First, in the top view of FIG. 8, assuming that the carbon fiber 5 isinclined by a length d1 in a lateral direction when the carbon fiber 5is wound by the section length d2 in the axial direction, the fiberangle ψ is expressed by the following Expression 2.

tan ψ=d1/d2  (Expression 2)

Next, in the side view of FIG. 8, the inclined surface 25 a of thetapered portion 25 extends by the section length d2 from the joinedsurface 40 a having the rising height t while being inclined at theinclination angle θ and intersects the outer peripheral surface 21 a ofthe general portion 21, and therefore, the inclination angle θ isexpressed by the following Expression 3.

tan θ=t/d2  (Expression 3)

Therefore, when d2 is deleted from Expression 2 and Expression 3, thefollowing Expression 4 is obtained.

tan θ/tan ψ=t/d1  (Expression 4)

Here, in the axial view of FIG. 8, the radius R (=the outercircumference radius R of the general portion 21) of the imaginary line40 b and the length d1 can be expressed by the following Expression 5 byusing a central angle η of the liner 3.

sin η=d1/R  (expression 5)

When both sides of Expression 5 are squared, the following Expression 6is obtained.

sin²η=(d1/R)²  (expression 6)

Further, in the side view and the axial view of FIG. 8, the relationshipbetween the radius R of the imaginary line 40 b and the rising height tcan be expressed by the following Expression 7 by using the centralangle η of the liner 3.

cos² η=R/(R+t)  (expression 7)

When both sides of Expression 7 are squared, the following Expression 8is obtained.

cos² η=R ²/(R+t)²  (expression 8)

In this way, when both sides of Expression 6 and Expression 8 are addedtogether and the central angle η of the liner 3 is deleted, thefollowing Expression 9 is obtained.

1=(d1/R)² +R ²/(R+t)²  (Expression 9)

When Expression 9 is arranged with respect to the length d1, thefollowing Expression 10 is obtained.

d1=R×(1−R ²/(R+t)²)^(1/2)  (Expression 10)

The above Expression 1 is obtained by substituting Expression 10 intoExpression 4 and arranging the obtained expression.

In this manner, when the inclination angle θ of the tapered portion 25(also called an ideal inclination angle θ) is determined by substitutingthe estimated level difference amount t (known), the fiber angle ψ(known), and the outer circumference radius R (known) of the generalportion 21 into Expression 1 calculated on the assumption that the gapbetween the liner 3 and the carbon fiber 5 is 0, theoretically, a gap isnot generated between the liner 3 and the carbon fiber 5.

Examples (Examples 1 to 4) of the ideal inclination angle θ actuallyobtained by calculation are shown in Table 1 below.

TABLE 1 Example 1 Example 2 Example 3 Example 4 Fiber angle Ψ (deg) 35.030.0 30.0 30.0 Outer 150.0 150.0 150.0 100.0 circumference radius R (mm)Estimated level 1.0 1.0 0.5 1.0 difference amount t (mm) Idealinclination 2.33 1.92 1.35 2.36 angle θ (deg)

Next, the effect that is obtained by setting the ideal inclination angleθ of the tapered portion 25 by using the above Expression 1 wasverified.

FIG. 9 is a conceptual diagram schematically describing the relationshipbetween a gap h between the liner 3 and the carbon fiber 5 and a setinclination angle ξ of the tapered portion 25. With respect to the setinclination angle ξ that is the same as the ideal inclination angle θ(Verification Example 1) in Example 1 of the above Table 1 and ten setinclination angles that are different from the ideal inclination angle θ(Verification Examples 2 to 11) set without using the above Expression1, the gap h between the liner 3 and the carbon fiber 5 was calculated.The results are shown in the following Table 2 and FIG. 10.

TABLE 2 Verifi- Verifi- Verifi- Verifi- Verifi- Verifi- Verifi- Verifi-Verifi- Verifi- Verifi- cation cation cation cation cation cation cationcation cation cation cation Exam- Exam- Exam- Exam- Exam- Exam- Exam-Exam- Exam- Exam- Exam- ple 1 ple 2 ple 3 ple 4 ple 5 ple 6 ple 7 ple 8ple 9 ple 10 ple 11 Fiber angle ψ 35.0 35.0 35.0 35.0 35.0 35.0 35.035.0 35.0 35.0 35.0 (deg) Outer 150.0 150.0 150.0 150.0 150.0 150.0150.0 150.0 150.0 150.0 150.0 circumference radius R (mm) Estimatedlevel 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 difference amount t(mm) Ideal inclination 2.33 2.33 2.33 2.33 2.33 2.33 2.33 2.33 2.33 2.332.33 angle θ (deg) Set inclination 2.33 4.65 6.98 9.31 11.63 13.96 16.2918.61 20.94 23.27 25.59 angle ξ (deg) Gap h (mm) 0.00 0.50 0.67 0.750.80 0.84 0.86 0.88 0.89 0.91 0.92

As shown in Table 2 and FIG. 10, in Verification Example 1 that is theset inclination angle ξ that is the same as the ideal inclination angleθ, it was confirmed that the gap h between the liner 3 and the carbonfiber 5 is 0 (mm). In contrast, in Verification Examples 2 to 11, it wasconfirmed that the gap h between the liner 3 and the carbon fiber 5increases and comes closer to the estimated level difference amountt=1.0 (mm) as the set inclination angle ξ gets away from the idealinclination angle θ.

In this manner, in this embodiment, it is possible to make the gapbetween the liner 3 and the carbon fiber 5 be 0 (mm), and therefore, asdescribed above, even though the height of the stepped surface 23 b isset to the maximum value of the gap allowable range, as shown in FIG. 7,occurrence of a harmful gap in the vicinity of the stepped surface 23 bcan be suppressed.

Next, modification examples of the embodiment described above will bedescribed. The following Modification Example 1 and Modification Example2 can also be applied to the domes 10, 30.

Modification Example 1

In the pipe 20 of the embodiment described above, the tapered portion 25and the general portion 21 are connected to each other simply by thestepped surface 23 b. However, as shown in FIG. 11, a corner portion 23c between the inclined surface 25 a and the stepped surface 23 b, and acorner portion 23 d between the outer peripheral surface 21 a of thegeneral portion 21 and the stepped surface 23 b may be set to be round.In this case, although the effect of making the boundary between thetapered portion 25 and the general portion 21 easier to be recognized isweakened, stress concentration due to a sudden change in thickness isalleviated, and therefore, there is an advantage that a decrease instrength can be reduced.

Modification Example 2

In the pipe 20 of the embodiment described above, the inclined surface25 a of the tapered portion 25 is made flat. However, as shown in FIG.12, an irregularity 25 b may be provided on the inclined surface 25 asuch that the fiber angle ψ can be reliably obtained with less frictionwhen the carbon fiber 5 is placed on the inclined surface 25 a. Thedepth of the irregularity 25 b is set within the allowable range of thegap between the liner 3 and the carbon fiber 5.

Other Embodiments

An applicable embodiment of the present disclosure is not limited to theembodiment above and can be implemented in various other forms withoutdeparting from the spirit or main characteristics of the presentdisclosure.

In the embodiment described above, the present disclosure is applied tothe liner 3 made of resin. However, there is no limitation thereto, andthe present disclosure may be applied to a liner made of metal.

Further, in the embodiment described above, the joining of the linerconstituent members 10, 20, 30 is performed by the infrared weldingmethod. However, there is no limitation thereto, and the joining of theliner constituent members 10, 20, 30 may be performed by, for example,welding or bonding using a laser, vibration, friction stirring, or thelike.

Further, in the embodiment described above, the three split-formed linerconstituent members 10, 20, 30 are joined to configure the liner 3.However, there is no limitation thereto, and for example, linerconstituent members divided into two or four or more parts may be joinedto configure a liner.

Further, in the embodiment described above, the outer shell is formedwith the carbon fiber 5. However, there is no limitation thereto, andthe outer shell may be formed with, for example, a glass fiber.

In this manner, the embodiment described above is merely exemplificationin all respects and should not be interpreted restrictively.

According to the embodiments of the present disclosure, it is possibleto suppress occurrence of a harmful gap between the liner and the fiberwhile the minimum plate thickness of the liner is secured, andtherefore, it is extremely useful for being applied to a method ofmanufacturing a high-pressure tank in which a fiber is wound around anouter periphery of a liner made by joining a plurality of parts, and thehigh-pressure tank.

What is claimed is:
 1. A high-pressure tank comprising: a linerconfigured by joining a plurality of cylindrical liner constituentmembers together; and a fiber wound around an outer periphery of theliner, wherein: the liner includes cylindrical general portions, and ajoined portion configured by joining joining end portions of thecylindrical liner constituent members together in an axial direction;the joined portion includes a first joining end portion and a secondjoining end portion, of which outer diameters at a joined surface areequal to each other; the first joining end portion has the samethickness as a thickness of the cylindrical general portion; and thesecond joining end portion has a larger outer diameter than thecylindrical general portion and is thicker than the cylindrical generalportion.
 2. The high-pressure tank according to claim 1, wherein thesecond joining end portion includes a tapered portion having an outerdiameter that decreases with increasing distance in the axial directionfrom the joined surface.
 3. The high-pressure tank according to claim 2,wherein an inclined surface of the tapered portion is stepped down to anouter peripheral surface of the cylindrical general portion before theinclined surface intersects the outer peripheral surface.